Blown Head Gasket? - pic

[Theee-Bopper]

I have a Volvo Penta AQ 125B with 270 outdrive on an 85 Bayliner. There is a spot just below the exhaust manifold ports where the head meets the block that is blowing air. It puffs the air out continuously, like a chuga chuga effect (feel & sound). If the boat is over-stressed (loaded with more than 4 adults) the air blowing out the hole will be smoky like its burning oil. I do occasionally have to top off the oil but it doesn?t seem to burn very much.
I suspect that this is a blown head gasket. Before it happened the oil pressure seemed to be running high (pegged out at 80 psi on the dash at usual cruising speed). Now the oil pressure generally runs about 70 psi on the dash at casual cruising speed. So my questions are:

(A.) Is this a blown head gasket? If so will I have to replace it or is there a way to patch it since it is possibly on an outer port? I am getting someone to do a compression test tonight to see if there is a noticeable change in compression across the pistons. The oil seems to be the right color by checking it with the dipstick.

(B.) If I have to replace it I need to figure out what caused the failure so it doesn?t just happen again. The boat is 28 years old so it could just be from old age. Any ideas?

 

[Don S]

Re: Blown Head Gasket? - pic

Pull the exhaust manifold off. Those engine would eat up the exhaust port in the head, and looks to be exactly what you have.
There used to be a kit to repair it, but I don't think they have it any more. A good welder and machine shop to flatten it down when done may be an option.

 

[jerryjerry05]

Re: Blown Head Gasket? - pic

Like Don said,the port's corroded and needs welding.
Also check the manifold for rusting through.
Sometimes they go hand in hand.

 

[Theee-Bopper]

Re: Blown Head Gasket? - pic

Thanks for your quick replies. In my rush to post before I left work yesterday I slipped up and put that it is around the exhaust manifold, but it?s actually on the intake manifold side between the 2 arm inlets closest to the heat exchanger. Does this probably change the previous preliminary diagnosis? Is it common for this engine to develop a leak or corrode around the intake manifold? I won?t be able to take off the inlet manifold until early next week to examine it.

 

[Alan Lloys]

Re: Blown Head Gasket? - pic

I have an AQ125B and have just restored an AQ125A.
I would start by taking the intake manifold off and see what the gaskets look like. Then make sure you clean all the old gasket material off and inspect for any corroded areas on the mating surfaces.
I had to do that on the AQ125A as it was sucking in "false" air making it run too lean at high RPM.

Be proactive and soak all the bolts and nuts with PB blaster or other rust loosening material for a day before you take it off.
The bolts have at nasty tendency to break off in the head. I had one break and I ended up drilling and tapping a new hole right next to the broken bolt. Not the correct way but it was basically a scrap engine I use to learn.
I also replaced the head gasket and lapped the valves when I had the head off.
BTW it runs pretty decent now on the test stand.